1. EXTREME STAR FORMATION IN THE LOCAL UNIVERSE

Extreme star formation is the violent, luminous star formation that
occurs in starbursts and luminous infrared galaxies. It is the formation
of super star clusters that may eventually become globular clusters. It
is the source of galactic winds and metal enrichment in galaxies. It is
probably what most star formation in the universe was like several
gigayears ago.

The process of star formation and its associated microphysics is most
easily studied in the local universe where we can examine the process
of star formation in detail. While there are regions in the Galaxy that
may qualify as extreme star formation, most extreme systems are
extragalactic. Advances in the study of extragalactic star formation
during the next decade are likely to come from improvements in spatial
resolution and sensitivity, particularly in the infrared and
submillimeter parts of the spectrum. The refurbished HST, forthcoming
JWST, and ground-based adaptive optics systems will make fundamental
contributions to our understanding of the stellar content of extreme
star forming regions. Herschel, ALMA, CARMA, Plateau de Bure, SMA, and
SOFIA are the far-infrared, submillimeter, and millimeter telescopes
that will deliver images and spectra of molecular gas in galaxies,
enabling the study of the earliest stages of star formation, and the
regulation of star formation by feedback into molecular clouds. With
the subarcsecond and milliarcsecond resolutions now possible we can
study the star formation process in other galaxies on the parsec
spatial scales of molecular cores, young clusters, and Stromgren spheres.

This review is an attempt to distill a very active area of research on
extreme star formation, covering both the stellar content and studies of
the star-forming gas, and to project this research into the observations
of the next decade. The field is a remarkably broad one, because in the
process of star birth and cluster evolution, stars and gas are
physically interrelated. The observations discussed here cover the range
from ultraviolet spectroscopy of hot stars to millimeter line imaging of
cold molecular clouds. The focus will be on star formation in the local
universe where individual star-forming regions can be resolved, and the
star formation process itself can be studied. Star formation in the
early universe, where extreme star formation may have been more the norm
than the exception, is covered elsewhere in this volume in contributions
by Tom Abel and Alice Shapley.